The current practice of orthodontics requires the use of brackets which are bonded to the teeth, or which are welded to stainless steel bands that encircle each tooth and are cemented in position. Each bracket is then ligated to an orthodontic archwire, which is periodically changed during the orthodontic treatment process. In the first place, an archwire may be adjusted by the dental practitioner in order to cause movement of the patient's teeth. In addition, elastic bands, or elastic chains and springs, can be attached to the bracket in order to move the teeth to a desired position along the orthodontic archwire.
The most popular type of orthodontic bracket is known as an edgewise bracket, which was introduced by Dr. Edward Angle in about 1925. There are two basic types of edgewise brackets, a single width edgewise bracket in which the body is cut across by an archwire slot, and a twin edgewise bracket, as shown in use in FIG. 1. Approximately 95% of all brackets that are in use in orthodontic treatment are edgewise brackets, and of these, about 90% are twin edgewise brackets.
Twin edgewise brackets are generally divided between standard edgewise brackets and preadjusted edgewise brackets. A standard twin edgewise bracket has a separation between the mesial and distal wings that is at right angles to the archwire slot. Moreover, the general outline of such a bracket from the facial or buccal view is square or rectangular. A preadjusted edgewise twin bracket, on the other hand, in most instances, has a rhomboid or trapezoid shape when viewed from the facial or buccal surface. Moreover, the slot between the wings of a preadjusted edgewise twin bracket is at an angle to the archwire slot.
In all edgewise brackets, as alluded to above, the archwire has to be ligated to the bracket in order to hold the archwire in place. This requires the use of a steel ligature wire, which is placed under the wing tips and over the archwire that is in the archwire slot. The two ends of the steel ligature are twisted together and cut off, leaving a little excess length to be bent under the archwire and close to the body of the bracket in order to avoid irritating the patient's tissues. The most common method of holding the archwire in place is by using a very small elastomeric plastic "O" ring, identified as 29 in FIG. 1, which is stretched under wing tips 25 of bracket 23 and over archwire 31 along both sides of bracket 23.
Ligating the archwire with a steel ligature is both time consuming and difficult. Moreover, if the patient later chews sticky or hard foods, the ends of the twisted ligature often bend outward and irritate the dental tissue, usually requiring an emergency visit to the orthodontic practitioner. While elastic ligatures avoid this problem, and are easily applied, even by moderately skilled dental personnel, they are less than desirable, since they degrade quickly in the mouth, and over a short period of time, loose their elasticity, preventing them from fully engaging the archwire in the archwire slot.
Synthetic elastomeric ligatures are usually made of the same material as elastomeric chains, and each "link" in the chain is essentially the same dimension as a single elastomeric ligature. In an article entitled "Synthetic Elastomeric Chains: A Literature Review" by David L. Baty et al. in The American Journal of Orthodontics and Dentalfacial Orthopractices in June, 1994, it was found that elastomeric chains generally lost 50% to 70% of their initial elasticity during the first day of location. Moreover, it was further found that elastomeric chains retain only 30% to 40% of original elasticity at the end of three weeks, which is the usual interval between orthodontic appointments for a patient. Furthermore, like elastic chains, synthetic elastomeric ligatures quickly degrade in the mouth and accumulate debris. This creates an unhygienic situation and an unsightly appearance, requiring frequent replacement of them.
Various mechanical self-locking or self-ligated brackets have been developed in the past. These brackets in general have limited versatility and acceptance. As can be appreciated, the orthodontic practitioner is normally well trained in the use of traditional twin edgewise brackets, and has developed various techniques to correct severe rotation, tipping and other malpositions of the teeth using these brackets.
Therefore, using a self ligating bracket instead of a conventional twin edgewise bracket is less than desirable. This is because such self-locking brackets are usually of the single width type and the dental practitioner will undoubtedly not have sufficient confidence that he can treat orthodontic cases with the same degree of perfection and ease as he could with a conventional twin edgewise bracket.
In addition, using a self ligating bracket is less than desirable because of the length of time (around two years) it takes to complete a standard orthodontic treatment. If the orthodontic practitioner uses a typical self-ligating bracket, and the results are not satisfactory, it may be necessary to remove the brackets from the patient's teeth, and replace them with the traditional twin edgewise type of bracket, which obviously is both time-consuming and costly.
Accordingly, the present invention enables the orthodontic practitioner to use a single or twin edgewise bracket, including a preadjusted edgewise bracket, yet still have the convenience and efficiency of a self-locking mechanism which can be easily removed as desired.